Investment Casting Materials and Manufacturing Process
Mold material
The performance of the molding material should not only ensure the convenient production of investment molds with accurate dimensions and high surface finish, good strength and light weight, but also create conditions for the manufacture of mold shells and good castings. Molding materials are generally formulated with waxes, natural resins and plastics (synthetic resins). All mold materials mainly prepared with wax materials are called wax-based mold materials, and their melting point is low, 60~70 ° C; all mold materials mainly prepared with natural resins are called resin-based mold materials, with a slightly higher melting point, about 70 °C. ~120℃.
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Manufacture of Folding Investments
In the production, the method of pressing the paste mold material into the mold is mostly used to manufacture the investment mold. Before pressing the investment, a thin layer of release agent should be applied to the surface of the embossing so that the investment can be removed from the embossing. When pressing wax-based molding materials, the parting agent can be engine oil, turpentine, etc.; when pressing resin-based molding materials, a mixture of sesame oil and alcohol or silicone oil is often used as a parting agent. The thinner the parting agent layer, the better, so that the investment mold can better replicate the surface of the embossing and improve the surface finish of the investment mold. There are three methods of pressing investment, plunger pressurization method, air pressure method and piston pressurization method.
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Assembly of Folding Investments
The assembly of the investment mold is to combine the investment mold that forms the casting and the investment mold that forms the gating riser system. There are two main methods:
1. Welding method Use a thin soldering iron to melt the joints of the investment to weld the investment together. This method is more common.
2. Mechanical assembly method In the mass production of small investment castings, the mechanical assembly method has been widely adopted abroad to combine modules. The use of this module can greatly improve the combination and efficiency of the modules, and the working conditions have also been improved.
The main processes and processes in the shell making process are:
1) Degreasing and degreasing of modules
In order to improve the ability of the coating to wet the surface of the module, the oil stain on the surface of the module needs to be removed when the wax-based moulding material is used to make the investment mould.
2) Apply paint and sand on the module
Before painting and hanging the paint, the paint should be stirred evenly to reduce the precipitation of refractory materials in the paint bucket as much as possible, and the viscosity or specific gravity of the paint should be adjusted so that the paint can fill and wet the investment mold well. The module is immersed in the paint and shakes up and down, so that the paint can well wet the investment mold and evenly cover the surface of the module. After the paint is applied, sanding can be carried out.
3) Shell drying and hardening
After each layer of shell is coated, it must be dried and hardened, so that the binder in the coating changes from sol to jelly and gel, and connects the refractory materials together.
4) Loss of investment from the shell
After the shell is completely hardened, the module needs to be melted from the shell. Because the module is usually made of wax-based mold material, this process is also called dewaxing. According to the different heating methods, there are many dewaxing methods, the hot water method and the same pressure steam method are used more.
5) Roasted shell
If molding (sand filling) is required for pouring, before firing, the demolded shell should be buried in the sand in the box, and then fired in a furnace. If the high temperature strength of the shell is high and no casting is required, the demolded shell can be directly sent to the furnace for roasting. During roasting, the furnace temperature is gradually increased, and the shell is heated to 800-1000 ° C and kept for a period of time before pouring.
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